Humidifying apparatus for warm air ducts and the like

ABSTRACT

An atomizing or spray type humidifier assembly to be removably mounted in an air conveying duct, such as a main trunk horizontal duct, of a hot air heating system. The humidifier assembly includes a solenoid controlled spray nozzle and a multi-layer screen supported in an elongated tunnel structure of rectangular cross-section having opposite open ends to be removably positioned wholly within the air conveying duct.

1.1111100 States Patent 1191 Marrow et a1.

HUMIDIFYING APPARATUS FOR WARM AIR DUCTS AND THE LIKE Inventors: WilliamB. Morrow, Winston-Salem; Gary H. Anders, Rural Hall, both of NC.

Aqua Mist, Incorporated, Winston-Salem, NC.

Filed: Jan. 3, 1973 Appl. No.: 320,818

Assignee:

us. (:1 261/100, 126/113, 261/116, 261/D1G. 15

1m. (:1 B0lf 3/04 Field 61 Search 261/98, 100, 105, 116, 261/126, DIG.15, 94, 95, 91; 126/113 References Cited UNITED STATES PATENTS 2/19159/1930 ll/l966 Ohnemus Vreeland .1

Allcorn, Jr 261/91 X 14 1 Dec; 17, 1974 3,290,021 12/1966 Blachly et a1.-261/91 X 3,334,877 8/1967 Payne 26l/D1Gj 15 3,516,647 6/1970 Jaffe eta1. 1 261/100 X 3,570,472 3/1971 Santangelo 126/113 3,605,388 9/1971Zuiderweg et a1. 261/126 X 3,689,037 /1972 Payne 26l/D1G. 15 3,770,25411/1973 Morrow 261/D1G. 15

Primary Examiner-Tim R. Miles Assista nt ExaminerRichard L. ChiesaAttorney, Agent, or Firm-Mason, Fenwick & Lawrence 5 7 ABSTRACT Anatomizing or spray type humidifier assembly to be removably mounted inan air conveying duct, such as a main trunk horizontal duct, of a hotair heating system. The humidifier assembly includes a solenoidcontrolled spray nozzle and a multi-layer screen supported in anelongated tunnel structure of rectangular cross-section having oppositeopen ends to be removably positioned wholly within the air conveyingduct.

13 Claims, 6 Drawing Figures BACKGROUND AND OBJECTS OF THE INVENTION Thepresent invention relates in general to humidifying apparatus for use inair conveying ducts, and more particularly to an atomizing or spray typehumidifier assembly having a valve controlled spray nozzle and amulti-layer screen supported in a structure adapted to be removablymounted in an air conveying duct, such as the main trunk horizontal ductof a hot air heating system, for use in association with a forcedcirculation warm air heating furnace or the like. v

Heretofore, various means have been employed to supply water vapor toheated air in wann air heating systems, such as forced circulation warmair furnaces of the domestic type, to increase the relative humidity ofthe air being supplied through the duct system to the living space. Oneof the common humidifier arrangements for use in connection with warmair furnaces has beenthe provision of an open tray or receptacle locatedin the bonnet or riser of the warm air furnace to be supplied with waterfor free evaporation of the water into the warm air in the bonnet orriser. This type of humidifier is of limited and usually inadequatecapacity, and becomes rapidly corroded or faulty and unreliable inoperation. In some cases, rotating belts, wheels or drums of varioustypes have been employed in the water-filled tray or receptacle to liftwater droplets into more effective thermal exchange relation with thewarm airin the bonnet. However, such moving belts, drums or screensrequire frequent cleaning and servicing, .due to deposits which rapidlyform because of the water in thelocality and minerals or chemicals inthe water, and provide another source of unreliable opera tion.

The furnace humidifier of the present invention is a simple unitaryinstallation comprising an open ended tubular humidifier chamber fixedin selected angular relation to a planiform mounting plate so as to liewithin the horizontal air conveying duct, such as the main trunkhorizontal duct extending from a furnace, to define an air flow tunnelextending along the direction of air flow within the duct. A spraynozzle is disposed adjacent the open upstream end of the tunnel memberto discharge towards the open downstream end of the tunnel member, and aplural layer wire mesh screen or similar foraminous member is supportedin the tunnel member at its downstream open end in the path of the spraydischarge from the nozzle to block the exit of water droplets from thetunnel member and to aid evaporation. The tunnel member is provided withmeans at the open upstream and downstream ends of the tunnel member toprevent loss of water droplets from the open ends and is provided withshort lengths of drain tubing at locations to collect and lead off waterwhich accumulates on the walls of the tunnel member to an externalcollecting facility. The tunnel member is fixed to the mounting plate ata selectedangular position and is simply installed by inserting thetunnel memher along a curved path through an opening 'cut in the heatingsystem duct wall which is only slightly larger than the cross-sectionalsize of the tunnel member and v is covered by the mounting plate whenthe tunnel mem- Spray diffusing nozzle systems which discharge a mist orfog of water dropletsintothe bonnet or riser area have also been used,usually with a target plate, a collecting trough, or some other similarfacility to collect unvaporized discharge from the nozzle. Many of thesespray diffusing nozzle systems have been difficult to control in such away as to reliably prevent unwanted discharge, such as drips,- from thenozzle following closber is inserted into the duct along a curvedinsertion path; The spray nozzle and solenoid control valve for thesupply pipe to the spray nozzle are supported by the mounting plate in aproper preassembled position so that the inlet to the solenoid valveneed merely be connected to an appropriate water supply.

An object of the present invention, therefore, is the provision of anovel atomizing typehumidifier device for use with air conveying ductsof a warm air heating system or the like which is simple in constructionand easy to install by the average homeowner or purchaser, which isextremely flexible permitting it to be mounted in a number of differentorientations, to dispose the tunnel portion thereof within the airconveying duct in ing of the supply valve regulating the water supply tothe nozzle. When the valve is spaced some distance from the spraynozzle, there is a pressure head remaining between the control-valve andthe nozzle when the valve closes. This pressure head'will cause thenozzle to spray and drip to some extent after the valve has closed. Suchunwanted discharge or drips accumulate in the furnace in normalinstallations and produce corrosive precipitate solids which adverselyaffect the life or operation of the furnace. The spray humidifiersystems have usually required complex special controls in addition tothe usual controls for the furnace, and for the most part have been toocomplex to be suitable for installation by the ordinary, unskilled homeowner as a do-it-yourself type of installation. If the spray humidifiersystem is to be readily adaptable to being installed by the averagehomeowner as a do-it-yourself installation, it is important that thehumidifier unit involve only a few components to be installed on thefurnace or ducting system and that it have provision for insuring thatno water can be accidentally discharged in the bonnet or riser region.

a position for the air to flow through the tunnel member, and which isreadily removable for replacement or cleaning of components which may besubject to contamination and provides highly reliable: humidity controlfor warm air furnaces of eitherthe electric, gas or oil type, heat pumpsystems, in a wide variety of types of furnace configurations andinstallation situations.

Other objects, advantages and capabilities of the present invention willbecome apparent from thefollowing detailed description, taken'inconjunction with the accompanying drawings illustrating a preferred embodiment of the invention.

BRIEF DESCRIPTION OF THE FIGURES FIG. 1 is a front perspective view ofthe atomizing humidifier unit of the present invention;

FIG. 2 is a horizontal longitudinal section view, to en- FIG. 3 is arear perspective view ofthe humidifier unit, viewed from the upstreamend of the tunnel member;

FIG. 4 is a rear perspective view of the humidifierunit, viewed from thedownstream end thereof;

FIG. 5 is a somewhat diagrammatic horizontal section view, illustratingpositions of the tunnel member of the humidifier unit as the same isswung through an opening in the warm air duct wall into final positionwithin the duct; and,

FIG. 6 is a somewhat diagrammatic vertical section view through a warmair duct, illustrating the position assumed by the humidifier wheninstalled through the bottom of the duct.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT Referring to thedrawings, wherein like reference characters designate correspondingparts throughout the several figures, the atomizing type humidifierassembly of the present invention is indicated generally by thereference character 10 and comprises a rigid, substantially rectangular,planiform mounting plate 11 having an outer face or surface 12 and aninner surface 13. An elongated humidifier tunnel member or open endedchamber 14 is carried in inclined relation by the mounting plate 11 withone edge, specifically the upstream edge of one wall, of the tunnelmember located against the inner surface 13. The tunnel member 14 is anelongated sheet metal member shaped to define a rectangularcross-section tunnel having an open downstream end 15 lying in a planeperpendicular to the longitudinal axis of the tunnel and an openupstream end 16 formed in a plane lying at an angle to the longitudinalaxis of the tunnel.

The sheet metal walls 14a, 14b, 14c and 14d defining the tunnel member14 are provided with inturned lips or barrier flanges 17 at the end 15and with inturned lips or barrier flanges 18 at the angular end 16 todefine water barriers at the downstream and upstream ends of the tunnelto confine any water accumulating on the inner surfaces of the tunnelwalls 14a-l4d to the interior of the tunnel. The tunnel wall 14a nearestthe mounting plate 11 is secured, as by spot welding or similarfastening means, at its edge bounding the upstream opening 16 to theinner surface of the mounting plate 11 and the wall 14a and tunnelmember 14 are maintained at a desired angle, for example about 5,relative to the plane of the mounting plate '11, by stand-off anglebrackets or members 20 having one flange welded or suitably affixed tothe mounting plate 11 against its inner surface 13 and the outerportions of the other flange weldedor suitably affixed to wall portionsof the tunnel member, for example the wall portions 14b and 14d.

Substantially centered just within the upstream end portion of thetunnel 14 along the center axis of the tunnel and directed downstream isa spray nozzle 22 mounted on a rigid right angle supply pipe, fonned forexample from a short stub section 23, a 90 ell 24 and a length of rigidwater supply pipe 25 extending through an accommodating aperture in thetunnel wall 14a and the mounting plate 11 to a solenoid valve 26. Theinlet of the solenoid valve is connected by an convenient conventionaltubing, indicated generally at 27, to a saddle valve or other means ofconnection to the house water line. A four layer wire screen is mountedwithin the tunnel member 14 immediately adjacent the downstream open end15, and may be conveniently formed from a length of screen wire about 31inches long by 6.5 inches wide, by forming eight transverse folds in thelength of screen wire and folding the same to the configurationillustrated in detail in FIG. 2. In one preferred embodiment, the lengthof screen is folded along eight transverse folds indicated at 31a, 31b,31c, 31d, 31e, 31f, 31g and 31h to produce four square screen panels 32,33, 34 and 35, each approximately 6.5 inches by 6.5 inches, with shortend spacer flanges 36 and short intermediate connector flanges 37, theflanges 37 in one preferred example being one inch wide and the flanges36 being /8 in. wide.

This humidifier unit is readily adaptable, by reason of its simplicity,and its flexibility as to orientation, to be installed by the averagehomeowner as a do-ityourself installation project. The installer merelycuts a rectangular or square opening 40, by following a template ordimensional directions which may be supplied with the humidifier kit, inan appropriate duct wall 41, either the horizontal bottom wall or one ofthe vertical side walls, of a horizontal warm air duct 42 such as themain trunk duct leading from the furnace indicated at 43 in FIG. 6. Forone example of the humidifier unit, wherein the humidifier chamber ortunnel 14 defines a square cross-section of approximately 6% inches by6% inches and the long side 14a is approximately 12 inches long, theopening 40 in the duct wall 41 may be about 7 inches by 7 inches. Thehumidifier unit may be readily mounted on the duct wall 41 by merelyinserting the end portion 15 of the humidifier chamber or tunnel portionthrough the opening 40 to the position indicated in solid lines in FIG.5, wherein the edge of the mounting plate 1 1 nearest the duct wallabuts or approximately abuts the duct wall 41. Then the humidifier unitis swung about an axis immediately adjacent or at the duct wall 41'through the successive positions indicated in broken lines in FIG. 5 tolocate the humidifier chamber portion 41 within the duct with the innersurface 13 of the mounting plate 11 outwardly abutting the portions ofthe duct wall bounding the opening 40. Four sheet metal screws 44 arethen inserted through corner openings in the mounting plate 11 and intothe underlying duct wall portions to fix the humidifier unit inposition.

It will be appreciated that the humidifier unit 10 can be mounted ineither of three basic configurations. It may be installed through thebottom wall of the duct, indicated at 41a in FIG. 6, by cutting theinsertion hole or opening 40 in the bottom horizontal wall 41a of theduct 42 and inserting the humidifier chamber or tunnel portion 14upwardly through the opening 40 to assume the position illustrated inFIG. 6. The downstream end 15 of the humidifier chamber or tunnelportion 14 may either be extended to the right of the opening 40 if theair flow direction is toward the right as viewed in FIG. 6 and indicatedby arrow 45, or it may be extended to the left of the opening 40 in casethe air flow through the duct 42 is in the opposite direction.Alternatively, the insertion hole or opening 40 may be provided ineither of the two vertical side walls 41b of the horizontal duct 42,with the humidifier chamber or tunnel portion 14 extending in adirection disposing the downstream end 15 either to the right of theopening 40 as viewed in FIG. 2, if the air flow is in the directionindicated by the arrow 46, or it may be located with the downstream end15 extending to the left of the opening 40 in case the air flow is inthe opposite direction from that indicated by the arrow 46 in FIG. 2.

Since the unit is provided with a pair of the short drain pipes 19extending through the sheet metal wall 14a at both transverse ends ofthe acute angle corner llda at the upstream end of the tunnel formation,so that the two drain pipes 1-9 are disposed at the top and bottom ofthe tunnel formation when itis mounted in mation extends to the right ofthe insertion opening 40 as illustrated in FIG. 2 or whether it extendsto the left of the insertion opening 40. Also the provision of thebarrier flanges or lips 17 and 18 at the downstream and upstream ends ofthe tunnel formation 14 extending inwardly from each of the four sidewalls forming the tunnel formation prevents any runoff at the upstreamand downstream ends of the tunnel formation of any drippage from thenozzle 22 or excess water dropping to the bottom surface of the tunnelformation from the screen 30, and confines this water to the humidifierchamber or tunnel zone so that the water ultimately is carried away byone of the drains 19. When the tunnel .formation 14 is mounted in theposition illustrated in FIG. 6 wherein the mounting plate is secured tothe bottom horizontal wall 41a of the duct, the inclined position of thelower wall 14a causes the water which drops onto the wall 14a, which isnow the bottom wall of the tunnel, to flow by gravity downwardly to thecorner 16a and out either of the drain pipes 119. The inclination of thewall 14a relative to the plane of the mounting plate 11 also enables thehumidifier to be inserted in the duct and shifted to the positionsillustrated in FIG. 5 through an opening which is only slightly I largerthan the cross-section of the tunnel formation .and can .be readilycovered by'the mounting plate 11.

The inlet conduit 27 to the solenoid valve 26 is readily connectable toa conventional house water line, as by providing a plastic tubeextending from the inlet of valve 26 or. from a short stub pipeextending from that inlet, with the other end of the tube connected by asaddle valve or other conventional means to an existing house waterline.

The electrical power for the solenoid valve .is typically derived fromthe furnace blower motor so that the solenoid valve 26 is opened onlywhen the furnace blower is operating. The solenoid valve can beconnected directly to a 120 volt circuit for the blower motor, or may beconnected through a step-down transformer to the blower motor so thatthe voltage supplied to the solenoid valve coil is only 24 volts,- atthe option serves to block the exit of water droplets from thehumidifier and into the furnace duct. At the same time,

air passing through the screen 30 will evaporate some I of the waterheld on the screen itself. Water in excess of that which is evaporateddrops to the bottom surface of the humidifier chamber or tunnel portion14 and is carried away by the drain 19. The installation may be readilymade by the home owner, and the unit may be readily removed from theduct and serviced, whenever required, without the need of skilled labor.

What is claimed is:

1. A humidifier assembly for use in association with a forcedcirculation warmair heating system including a horizontal heated airsupply duct section communicating with a furnace and having a flat ductwall portion having an insertion opening formed therein, the humidvifier assembly comprising a' rigid planar mounting plate of a size tocover said insertion opening having edge portions to overlie the ductwall' portions bounding said opening and be fastened thereto, anelongated tunnel duct member of .four fiat solid sheet metal tunnelwalls of greater length than the dimension of the insertion of theinstaller. Also, if desired, a humidistat control of conventionalconstruction may be insertedin electrical series with the solenoid valveso that the humidifier will only spray when the furnace blower isoperating and the ambient humidity is below the humidistat setting, oris operated when the furnace blower is operating and the humidistat isset to the ON position if the humidistat has such a setting.

With the installation wired either directly to the fur nace blower motoror in series with a humidistat control to the fumace blower motor, thesolenoid valve 26 is opened to supply water to the atomizing nozzle 22whenever the furnace operates (and when humidity is called for if ahumidistat is included in the circuit). The

opening along the direction of air flow in the duct section joinedtogether along their-longitudinal edges and defining an elongatedhumidifier tunnel of rectangular cross-section extending along arectilinear tunnel axis inclined at a sharp angle to the plane of saidmounting plate and having opposite open ends forming upstream anddownstream end portions of the tunnel, means fixing said duct member tosaid mountingplate to locate the tunnel wholly within the duct sectionwith a wall of the duct member supported against the mounting plate forflow of heated duct air there'through with the downstream end portionlocated downstream beyond said opening when the mounting plate ispositioned in covering relation to the opening, a spray discharge nozzlecoupled through a valve to a water source and located within the tunneladjacent its upstream end for discharging a mistlike spray pattern ofwater droplets in a downstream direction within the tunnel, and anevaporation screen supported within said tunnel downstream of saidnozzle in the path of saidwater droplets to collect droplets thereon andevaporate them into the air flowing through the tunnel.

2. A humidifier assembly as defined in claim 1,

wherein said tunnel walls have barrier flanges at the up-. stream anddownstream edges thereof extending toward the center axis of the tunnelto retain within the tunnel any drippagefrom the nozzle or excess waterrunoff from'the screen.

3. A humidifier assembly as defined in claim 2, including drain pipemeans extending through a selected wall of the tunnel and outwardlythrough said mounting plate to communicate with the region within thetunnel where water dripping from the nozzle or'screen may collect todrain such water to the exterior of the duct.

4. A humidifier assembly as defined in claim 2,

wherein the tunnel wall adjacent the mounting plate is joined thereto atthe upstream edge of the tunnel wall, the upstream edges of said tunnelwalls lying in a plane inclining inwardly of the ductsection from themounting plate in a downstream direction at an angle of subthrough themounting plate into the tunnel at the juncture of said mounting plateand upstream edge of the adjacent tunnel walls to withdraw wateraccumulations from within the tunnel.

5. A humidifier assembly as defined in claim 4, wherein said drain pipemeans comprises a pair of drain pipes located at the opposite transverselimits of the upstream edge of said selected wall to dispose said drainpipes immediately inwardly adjacent the top and bottom wallsrespectively of the tunnel when the mounting plate is mounted against avertical side wall of the duct.

6. A humidifier assembly as defined in claim 2, wherein said screen is awire mesh screen having a plurality of rectangular, parallelsubstantially planar screen panels and each vertically and horizontallyspanning the tunnel in planes perpendicular to the tunnel axis adjacentthe downstream end of the tunnel.

7. A humidifier assembly as defined in claim 1, including drain pipemeans extending through a selected wall of the tunnel and outwardlythrough said mounting plate to communicate with the region within thetunnel where water dripping from the nozzle or screen may collect todrain such water to the exterior of the duct.

8. A humidifier assembly as defined in claim 7, wherein said drain pipemeans comprises a pair of drain pipes located at the opposite transverselimits of the up- 9. A humidifier assembly as defined in claim 1,wherein the tunnel wall adjacent the mounting plate is joined thereto atthe upstream edge of the tunnel wall,

the upstream edges of said tunnel walls lying in a plane inclininginwardly of the duct section from the mounting plate in a downstreamdirection at an angle of substantially less than ninety degrees to themounting plate plane to define an air inlet opening to the tunnel at itsupstream end of larger area than the cross sectional area of the tunnel.

10. A humidifier assembly as defined in claim 9, wherein said screen isa wire mesh screen having a plurality of rectangular, parallelsubstantially planar screen panels folded from a single length of screenand each vertically and horizontally spanning the tunnel in planesperpendicular to the tunnel axis adjacent the downstream end of thetunnel.

11. A humidifier assembly as defined in claim 9, wherein said drain pipemeans comprises a pair of drain pipes located at the opposite transverselimits of the upstream edge of said selected wall to dispose said drainpipes immediately inwardly adjacent the top and bottom wallsrespectively of the tunnel when the mounting plate is mounted against avertical side wall of the duct.

12. A humidifier assembly as defined in claim 11, wherein said screen isa wire mesh screen having a plurality of rectangular, parallelsubstantially planar screen panels folded from a single length of screenand each vertically and horizontally spanning the tunnel in planesperpendicular to the tunnel axis adjacent the downstream end of thetunnel.

13. A humidifier assembly as defined in claim 1, wherein said screen isa wire mesh screen having a plurality of rectangular, parallelsubstantially planar screen panels and each vertically and horizontallyspanning the tunnel in planes perpendicular to the tunnel axis adjacentthedownstream end of the tunnel.

1. A humidifier assembly for use in association with a forcedcirculation warm air heating system including a horizontal heated airsupply duct section communicating with a furnace and having a flat ductwall portion having an insertion opening formed therein, the humidifierassembly comprising a rigid planar mounting plate of a size to coversaid insertion opening having edge portions to overlie the duct wallportions bounding said opening and be fastened thereto, an elongatedtunnel duct member of four flat solid sheet metal tunnel walls ofgreater length than the dimension of the insertion opening along thedirection of air flow in the duct section joined toGether along theirlongitudinal edges and defining an elongated humidifier tunnel ofrectangular cross-section extending along a rectilinear tunnel axisinclined at a sharp angle to the plane of said mounting plate and havingopposite open ends forming upstream and downstream end portions of thetunnel, means fixing said duct member to said mounting plate to locatethe tunnel wholly within the duct section with a wall of the duct membersupported against the mounting plate for flow of heated duct airtherethrough with the downstream end portion located downstream beyondsaid opening when the mounting plate is positioned in covering relationto the opening, a spray discharge nozzle coupled through a valve to awater source and located within the tunnel adjacent its upstream end fordischarging a mistlike spray pattern of water droplets in a downstreamdirection within the tunnel, and an evaporation screen supported withinsaid tunnel downstream of said nozzle in the path of said water dropletsto collect droplets thereon and evaporate them into the air flowingthrough the tunnel.
 2. A humidifier assembly as defined in claim 1,wherein said tunnel walls have barrier flanges at the upstream anddownstream edges thereof extending toward the center axis of the tunnelto retain within the tunnel any drippage from the nozzle or excess waterrunoff from the screen.
 3. A humidifier assembly as defined in claim 2,including drain pipe means extending through a selected wall of thetunnel and outwardly through said mounting plate to communicate with theregion within the tunnel where water dripping from the nozzle or screenmay collect to drain such water to the exterior of the duct.
 4. Ahumidifier assembly as defined in claim 2, wherein the tunnel walladjacent the mounting plate is joined thereto at the upstream edge ofthe tunnel wall, the upstream edges of said tunnel walls lying in aplane inclining inwardly of the duct section from the mounting plate ina downstream direction at an angle of substantially less than 90* to themounting plate plane to define an air inlet opening to the tunnel at itsupstream end of larger area than the cross sectional area of the tunnel,and exterior drain pipe means extending through the mounting plate intothe tunnel at the juncture of said mounting plate and upstream edge ofthe adjacent tunnel walls to withdraw water accumulations from withinthe tunnel.
 5. A humidifier assembly as defined in claim 4, wherein saiddrain pipe means comprises a pair of drain pipes located at the oppositetransverse limits of the upstream edge of said selected wall to disposesaid drain pipes immediately inwardly adjacent the top and bottom wallsrespectively of the tunnel when the mounting plate is mounted against avertical side wall of the duct.
 6. A humidifier assembly as defined inclaim 2, wherein said screen is a wire mesh screen having a plurality ofrectangular, parallel substantially planar screen panels and eachvertically and horizontally spanning the tunnel in planes perpendicularto the tunnel axis adjacent the downstream end of the tunnel.
 7. Ahumidifier assembly as defined in claim l, including drain pipe meansextending through a selected wall of the tunnel and outwardly throughsaid mounting plate to communicate with the region within the tunnelwhere water dripping from the nozzle or screen may collect to drain suchwater to the exterior of the duct.
 8. A humidifier assembly as definedin claim 7, wherein said drain pipe means comprises a pair of drainpipes located at the opposite transverse limits of the upstream edge ofsaid selected wall to dispose said drain pipes immediately inwardlyadjacent the top and bottom walls respectively of the tunnel when themounting plate is mounted against a vertical side wall of the duct.
 9. Ahumidifier assembly as defined in claim 1, wherein the tunnel walladjacent the mounting plate is joined thereto at the upstream edge ofthe tunnel wall, the upstream edges of said tuNnel walls lying in aplane inclining inwardly of the duct section from the mounting plate ina downstream direction at an angle of substantially less than ninetydegrees to the mounting plate plane to define an air inlet opening tothe tunnel at its upstream end of larger area than the cross sectionalarea of the tunnel.
 10. A humidifier assembly as defined in claim 9,wherein said screen is a wire mesh screen having a plurality ofrectangular, parallel substantially planar screen panels folded from asingle length of screen and each vertically and horizontally spanningthe tunnel in planes perpendicular to the tunnel axis adjacent thedownstream end of the tunnel.
 11. A humidifier assembly as defined inclaim 9, wherein said drain pipe means comprises a pair of drain pipeslocated at the opposite transverse limits of the upstream edge of saidselected wall to dispose said drain pipes immediately inwardly adjacentthe top and bottom walls respectively of the tunnel when the mountingplate is mounted against a vertical side wall of the duct.
 12. Ahumidifier assembly as defined in claim 11, wherein said screen is awire mesh screen having a plurality of rectangular, parallelsubstantially planar screen panels folded from a single length of screenand each vertically and horizontally spanning the tunnel in planesperpendicular to the tunnel axis adjacent the downstream end of thetunnel.
 13. A humidifier assembly as defined in claim 1, wherein saidscreen is a wire mesh screen having a plurality of rectangular, parallelsubstantially planar screen panels and each vertically and horizontallyspanning the tunnel in planes perpendicular to the tunnel axis adjacentthe downstream end of the tunnel.